Flexible Axle Comprising a Cross-Member with Trapezoid Cross-Section, Corresponding Cross-Member, Vehicle and Manufacturing Method

ABSTRACT

A flexible axle for motor vehicle has a cross-member ( 1 ) connecting two longitudinal arms ( 2 ), wherein said cross-member ( 1 ) has a closed cross-section, and said cross-member has, at least in a central zone, a substantially trapezoid cross-section ( 11 ).

CROSS-REFERENCE TO RELATED APPLICATION

This Application is a Section 371 National Stage Application ofInternational Application No. PCT/EP2005/056618, filed Dec. 8, 2005, andpublished as WO 2006/061424 A1 on Jun. 15, 2006, not in English.

The field of the disclosure is that of motor vehicles. More precisely,the disclosure concerns flexible axles for motor vehicles.

Let us recall that what is called a flexible axle generally refers to anaxle designed to form a torsion element between two wheels.

Classically, a flexible axle comprises two longitudinal arms each ofthem bearing the wheel mountings and connected by a transversal linkingelement known as the cross-member axle, dead axle or profile axle.

During the design of an axle, two quantities, among others, areconsidered when appreciating the qualities of the axle: flexing andtorsion.

The principle of flexible axles allows the reconciling of a highstiffness to flexing with a relative flexibility to torsion. In general,it is through the geometries of the cross section of the cross-member,via its flexion and torsion inertia, that a desired compromise isobtained between stiffness to flexing and flexibility (relative) totorsion.

The cross sections selected to produce steel axles (or other isotropicmaterials) have often “V”, “U”, or “L” shapes, since these types ofgeometric provide an interesting relationship between flexion andtorsion inertia.

Recent years have seen the large scale deployment of the technique offlexible axles in segments of the lower and medium range automobileconstruction, thanks to its numerous advantages, among which are anexcellent service duty/architecture compromise, and economicimplementation principally employing mechanical welding type assemblies.

These advantages lead suspension designers to continually push thetechnique towards more and more refinement. The flexible axles are infact prone to a certain number of limitations among which is a delicatecompromise between longitudinal and transversal stiffness and adurability conditioned by the endurance behaviour of both componentswhich are subject to large elastic deformations.

The continually rising demand for comfort and road holding points thedesign of flexible cross-member axles towards solutions consisting ofintroducing a torsion stiffness element between the two trailing arms,commonly known as an “anti-roll bar” or “Panhard rod”, with the aim oflimiting the canting of the vehicle while preserving great verticalflexibility of the suspension train, guaranteeing a filtering out ofroad imperfections from the chassis.

But the continual enlarging of the perimeter of applying the techniqueof flexible axles to high mass vehicles (large saloon cars, mini vans,people carriers and even utility vehicles) without lowering the qualityof the ride, continually leads to components that are working withintheir absolute limits of operation, whether through static resistance toincidental forces, or metal fatigue behaviour during the life cycle ofthe suspension train.

The linking element, or cross-member, is thus one of the most difficultcomponents to design, particularly from the point of view of enduranceand behaviour.

At present, on flexible cross-member axles, the cross-member linking thelongitudinal arms are produced using two different technologies.

In one technology, the cross-member is manufactured from a bent section(or pressed steel) in such a way as to procure a cross section having anU-shaped, V-shaped or L-shaped form. These cross-members generally haveto be associated with an anti-roll bar, to provide torsion stiffness tothe axle.

The second technology consists of integrating the anti-roll stiffnessfunction in the cross-member itself.

In this case, the cross-member is manufactured from a tube, generallyhaving a circular section, with the tube then being submitted, at leastin its central part, to a deforming process in which a portion of thewall is crushed inwards towards another portion of the wall in order toprovide the desired stiffness torsion and flexion (example: Peugeot806®, illustrated in FIG. 1, or the Opel Zafira®, illustrated in FIG.2).

The diversity of anti-roll stiffness in function of the needs is ensuredby modifying the cross section of the cross-member.

This disclosure applies to axle cross-members produced according to thissecond technology, those currently designated by the term “closedprofile axles” or “closed section axles”.

In a general manner, the disclosure applies to all flexible axles usinga cross-member constituted from a tube having in its central region aconcavity with U-shaped or V-shaped cross section.

The tube of the cross-member is only crushed in one transversal portionto reduce torsion, and retains its circular sections at the extremities,in order to facilitate the connection to the suspension arms viawelding.

Moreover, the cross-members of these axles possess at least onerectilinear generatrix of the profile that links the two extremities.

This traditional design of closed section cross-members has theconsequence that the centre of torsion of the median section cannot bevery far from the initial axis of the tube, due to its geometry. Only arotation of the cross-member around its axis permits any angularmodification of the centre of torsion position.

But certain requirements of vehicle manufacturers as to the behaviour ofthe axle are incompatible with a low offset between the centre oftorsion of the axle and the axis of the tube constituted by the centresof the circular sections at its extremities.

In fact, the degree of travel induced by a rolling movement is such thatit requires an important vertical translation of the central section.

Furthermore, this incompatibility is in certain cases accentuated byarchitecture constraints. These constraints in fact lead, in certaincases, to reconsidering the space occupied by the cross-member inrelation to the exhaust pipe.

SUMMARY

One aspect of the present disclosure is a flexible axle for motorvehicles, and comprises a cross-member linking two longitudinal arms,characterised by said cross-member having a closed section, and in thatsaid cross-member presents, at least in one central region, a section ofa significantly trapezoid shape.

In this manner, we significantly offset the centre of torsion of theaxle in relation to an axis corresponding to the axis of the tube beforeits deformation.

The behaviour of the corresponding axle is thus considerably improved.

According to one preferred embodiment, said cross-member presents a bentsection, said cross-member preferably having at each of its extremitiesa circular section.

According to one preferred embodiment, the centre of inertia of thecentral section of said cross-member is distant from a straight linepassing through the inertia centres of the sections of the extremitiesof said cross-member.

In this manner a bending of the cross-member is achieved and its effectis added to that of the trapezoid cross section of the cross-member inits central region, thus contributing to increasing the offset of thecentre of torsion and, consequently, to the stiffness of the axle.

Moreover, the sections of the extremity of the cross-member may thus bepositioned beneath an exhaust pipe in an architecture according to whichthe path of the exhaust pipe passes above the cross-member by goingabove a section of the extremity of the cross-member on the left handside of the vehicle.

In one aspect, the disclosure equally concerns a cross-member intendedto link two longitudinal arms on a flexible axle of a motor vehicle, andcharacterised in that it has a closed section and in that saidcross-member presents, at least in one central region, a section that issignificantly trapezoid in shape.

In one aspect, the disclosure also concerns a vehicle equipped with aflexible axle for motor vehicle, comprising a cross-member linking twolongitudinal arms, and characterised in that said cross-member has aclosed section, and in that said cross-member presents, at least in onecentral region, a section that is significantly trapezoid in shape.

In one aspect, the disclosure likewise concerns a procedure formanufacturing a cross-member intended to cross link the two longitudinalarms of a motor vehicle flexible axle, and characterised in that it hasa manufacturing step consisting of deforming a cross-member with aclosed section in such a manner that said cross-member presents, atleast in one central region, a section that is significantly trapezoidin shape.

Preferably, the procedure comprises a deformation phase of saidcross-member providing a bent section between its central region and itstwo extremity sections.

According to one advantageous embodiment, said deformation phase iscarried out in two steps, one consisting of producing a pre-deformationin at least one transition zone between said central region and a regionof circular section close to at least one of its extremities, the otherstep consisting of continuing the deformation in said central region inorder to confer its final shape.

Advantageously, said deformation phase is carried out via pressing.

Preferably, the procedure comprises a step consisting of bending saidcross-member in such a manner that the centre of inertia of the centralsection of said cross-member is distant from a straight line passingthrough the centre of inertia of the sections at the extremities of saidcross-member.

Other characteristics and advantages of the subject matter of thisdisclosure will appear more clearly on reading the following descriptionand according to a preferred mode of producing a flexible axle, givenhere by way of an illustrative and non limitative example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are each views of an axle comprising a cross-member withclosed section according to prior art.

FIG. 3 is a perspective view of a flexible axle according to the presentdisclosure.

FIG. 4 is a perspective view of the cross-member of a flexible axleaccording to the present disclosure.

FIG. 5 is a partial view of the axle according to the present disclosureas illustrated in FIG. 3.

FIG. 6 is a view of two transversal sections of the cross-member of anaxle according to the present disclosure.

DETAILED DESCRIPTION

As mentioned previously, the principle of the present disclosure is thefact of producing a flexible axle with the aid of a cross-member whoseclosed section presents, at least in the central region of thecross-member, a notably trapezoid section.

By central region, is meant a portion of the length of the cross-membermore or less extended, and centered between the two extremities of thecross-member.

This is illustrated in FIG. 3 which shows such a flexible axlecomprising a cross-member, as previously mentioned, linking the twolongitudinal arms 2.

You are reminded that the axle is connected to the body of the vehiclevia articulated bushed links 21 borne in the longitudinal arms 2, theselatter each present at their extremity bushes 21, and an axle head 22intended to bear a turning part.

As shown in FIG. 5, each axle head 22 is, according to the presentembodiment, made solid with:

-   -   a spring seat 221    -   a clevis 222 for fixing a Panhard Bar®    -   a thrust piece 223 for a spring seat.

Each axle head 22 has as well a means of fixing 223 intended forattaching a shock absorber to the axle.

We also note that each arm 2 comprises a forward part (bearing bush 21)fixed by bolts to the axle head 22.

In reference to FIG. 4, an axle cross-member according to the presentdisclosure has a central part with a trapezoid section 11 (shown by thedark line in FIG. 4).

Moreover, the section of the cross-member is formed in such a way thatit progressively changes from the trapezoid shape in its central part toa circular shape at its extremities 12.

Furthermore, cross-member 1 has a bent shape. In other words, thecross-member presents a longitudinal deformation produced in such a waythat the centre of inertia at the median level of the cross-member isoffset in relation to a straight line connecting the centres of circularextremity sections 12.

Thus, on such a described cross-member, the centre of torsion of thecentral section, and all the connected deformed sections, is offsetupwards to the maximum in order to obtain an equivalent centre oftorsion as high as possible.

By equivalent centre of torsion of the cross-member is meant all thepositions of the centres of torsion of all the sections of thecross-member.

A cross-member, such as is shown in FIG. 4 is produced by metal formingdeformation of the cross-member in order to obtain the maximum offset ofthe central section while conserving a radius of curvature as great aspossible while mastering the process.

FIG. 6 shows, in cross section, the positioning of the trapezoid section11 in the median plane (note Y=0) of the axle in relation to theextremity sections 12.

The following elements are shown in this Figure:

-   -   T_(o), which represents the centre of torsion of the median        section of the axle;    -   G_(o), which represents the centre of inertia of the median        section of the axle;    -   G₁, which represents the centre of inertia of extremity section        12.

We note, as clearly shown, that points T_(o), G_(O) and G₁ are aligned.

Moreover, the metal forming deformation in direction Z leads to thesides H (between G_(O) and G₁) and d (between T_(o) and G₁) beingdetermined in such a way as to optimise the position of T_(o) indirection Z, i.e., to maximise distance d.

To manufacture an axle in the previously described manner, steps arecarried out that consist of:

-   -   cutting a circular section tube to a predetermined length;    -   bending the tubular length thus obtained by fixing its two        extremities and applying, with the aid of a press, a force        significantly perpendicular to the axis of the tubular section;    -   deforming the curved section in such a way that it presents a        bowed section in its central section which is significantly        trapezoid.

It is noted that the deformation phase is carried out in two steps:

-   -   one consisting of preparing a transition zone between the final        central region and the circular section (i.e., a non deformed        region at the end of the deformation phase) and close to the        extremities of the cross-member;    -   the other consisting of pressing the pre-deformed cross-member        in order to obtain the desired trapezoid shape for the central        section of the cross-member.

The present disclosure is directed to the aim of providing a flexibleaxle whose closed profile cross-member permits a considerable increasein the torsion stiffness of the axle in relation to solutions of theprior art.

The disclosure equally aims to provide an axle that can be adapted tonew architectures, particularly in relation to the positioning of theexhaust pipe.

The disclosure also aims to provide a manufacturing procedure for thecross-member of such an axle.

1. A flexible axle for a motor vehicle, comprising a cross-member (1)linking two longitudinal arms (2), wherein said cross-member (1)possesses a closed section, and in which said cross-member has, at leastin a central region, a section that is trapezoid in shape (11).
 2. Aflexible axle according to claim 1, wherein the cross-member (1) has abent section.
 3. A flexible axle according to claim 1, wherein saidcross-member (1) has at each of its extremities a circular section (12).4. A flexible axle according to claim 2, wherein a centre of inertia(G_(O)) of the central section of said cross-member is distant to astraight line passing through the centres of inertia (G_(i)) of thecircular sections (12) of said cross-member (1).
 5. An axle cross-memberintended to link two longitudinal arms on the flexible axle of a motorvehicle, comprises in one central region, a section of trapezoid shape(11).
 6. A vehicle equipped with a flexible axle for a motor vehicle,comprising a cross-member (1) linking two longitudinal arms (2), whereinsaid cross-member possesses a closed section, and said cross-memberpossesses, in a central region, a section of trapezoid shape (11).
 7. Amanufacturing method for a cross-member (1) intended to link twolongitudinal arms (2) on a flexible axle of a motor vehicle, comprising:deforming the cross-member having a closed section in such a manner thatsaid cross-member possesses, in one central region, a section oftrapezoid shape (11).
 8. The manufacturing method according to claim 7,comprising a deformation phase of said cross-member carried out in sucha manner as to form a bent section between its central region and itstwo extremity sections.
 9. The manufacturing method according to claim8, wherein said deformation phase comprises: carrying out apre-deformation in at least one transition zone between said centralregion and a circular section region in the region of at least one ofits extremity sections; and continuing the deformation in said centralregion in order to give it its final shape.
 10. The manufacturing methodaccording to claim 8, wherein said deformation phase is carried out bypressing.
 11. The manufacturing method according to claim 8, comprising:bending said cross-member in such a manner that the centre of inertia ofthe central region of said cross-member is distant to a straight linepassing through the centres of inertia of the extremity sections of saidcross-member.